In an air injection type weaving machine among automatic weaving machines of a fluid injection type, a sub-nozzle jetting high-speed air flow is installed in addition to a main nozzle for wefting. This sub-nozzle prevents weft supplied from the main nozzle from stalling when it is flying in openings of warp. A nozzle head goes in and out of the openings of warp in an oscillating motion to provide an injection timing of air synchronized with the flying of weft.
A typical structure of such a sub-nozzle includes a distal end of a pipe with a blind hole formed by a deeply drawn metal plate, which is flattened where an injection hole of air is opened.
The most serious problem in using a sub-nozzle is that the surface of the nozzle head thereof is brought into contact with warp in oscillation, causing wear of the nozzle head or damage of warp. Burrs or the like are apt to occur on the surface of a sub-nozzle made of a metal and their adverse influence on warp has been unavoidable.
To resolve these problems a hard film is formed on the surface of the sub-nozzle to increase wear resistance as disclosed in Japanese Unexamined Patent Publication No. Sho 59-106541. Further, a sub-nozzle in which the nozzle head is formed by a composite material (cermet) of metal and ceramics has already become known as described in Japanese Unexamined utility model Publication No. Sho 62-28887.
Further, according to Japanese Unexamined Patent Publication No. Sho 63-264947 there has been proposed a sub-nozzle in which the nozzle head thereof is integrally formed by a partially stabilized zirconia ceramic to prevent damage of the warp by contact with the surface of the sub-nozzle, in which the total surface constitutes one smooth face to prevent fluff of warp.
However, in a sub-nozzle on which a surface treatment of hard film is provided, metal matrix may be exposed by partial separation, wear of the hard film due to deterioration, or lowering of other mechanical strengths etc. It is highly possible that warp is damaged by being caught at the exposed portions.
Meanwhile, in a sub-nozzle in which the nozzle head is integrally formed by cermet or ceramics, a sufficiently favorable result has been obtained with respect to wear resistance, and its influence on warp is insignificant.
However, it is indispensable that a nozzle head be provided with mechanical strength when forming a sub-nozzle of such a material. Therefore, a strong and dense material is required, and very careful flow control is necessary in manufacturing from the raw material powder stage to the final forming stage. Further, a thin-walled product has been required to respond to the downsizing of nozzle heads. In such a thin-walled product, deformations or cracks thereof occur and, further, a number of defective products caused by dispersion of the shrinkage rate in sintering, over-sintering, or under-sintering are brought about. Further, since a nozzle made of cermet or ceramics is especially hard, numerous lapping steps are required to decrease the surface roughness of the nozzle head.
As stated above, warp is adversely influenced by a sub-nozzle in which the surface of the nozzle head is treated by a hard film, whereas in a sub-nozzle in which the nozzle head is integrally formed by cermet or ceramics, there are a number of manufacturing problems in yield, working steps, and quality control which increase the production costs in comparison with those of nozzles made of metal.
It is an object of the present invention to provide a sub-nozzle for an automatic weaving machine which does not cause fluffing or the like through contact with warp, and for which manufacturing control is facilitated.